1. Field of the Invention
The invention relates to the use of specified chloromethyl chloropyridines as antidotes or safeners for the protection of valuable crops from unwanted herbicidal action or stress on the crops upon the application of a thiocarbamate herbicide such as S-ethyl diisobutylthiocarbamate or S-ethyl dipropylthiocarbamate or the herbicide 2-(2,2,2-trichloroethyl)-2-(3,5-dichlorophenyl)oxirane applied to the locus of the valuable crops and to a herbicidal composition containing at least one of said chloromethylchloropyridines and one of the referenced herbicides.
2. Description of Prior Art
The known herbicide compounds exhibit a spectrum of activity against various weed species and crops. The extent of herbicidal action varies from plant species to plant species and a dosage rate of herbicidal compound which is tolerated by a given valuable crop may not be sufficient to permit control of each of the weed species that are usually encountered in growing the specified crop. Sometimes a combination of two or more herbicide compounds will provide an improved spectrum of weed control without exceeding good crop tolerance.
Another approach to facilitating broad spectrum weed control without exceeding crop tolerance is to employ an antidote or safener compound which selectively improves the tolerance of one or more valuable crops without substantially diminishing the herbicidal action of the herbicidal compound against the weed species it is desired to control.
Butylate, i.e., S-ethyl diisobutylthiocarbamate is a well-known herbicide active against some of the annual and perennial grassy weeds as well as some of the broad leaf weeds in the presence of crops such as sweet corn, field corn and cotton, as described in Herbicide Handbook of the Weed Science Society of America, Third Edition, Weed Science Society of America, Champaign, Ill., 1974 at page 77.
EPTC, i.e., S-ethyl dipropylthiocarbamate is a well-known herbicide used for the control of some of the annual grassy weeds as well as some of the broad leaf weeds in the presence of crops such as alfalfa, garden produce, citrus corn and cotton crops. EPTC is further described starting at page 179 of the referenced Herbicide Handbook.
Molinate, i.e., S-ethyl hexahydro-1H-azepine-1-carbothioate, is a well-known herbicide active against some of the annual grassy weeds and broadleaf weeds in the presence of crops, particularly rice, as described in said Herbicide Handbook.
Vernolate, i.e., S-propyl dipropylthiocarbamate, is a well-known herbicide active against some of the annual grassy weeds and broadleaf weeds in the presence of crops such as soybeans, peanuts, tobacco and sweet potatoes, as described in said Herbicide Handbook.
Cycloate, i.e., S-ethyl cyclohexylethylthiocarbamate, is a well-known herbicide used for the control of some annual grassy weeds and broadleaf weeds in the presence of crops such as sugarbeets, spinach and table beets, as described in said Herbicide Handbook.
Pebulate, also referred to as PEBC, i.e., S-propyl butylethylthiocarbamate, is a well-known herbicide useful for the control of some grassy weeds and broadleaf weeds in the presence of crops such as sugarbeets, tomatoes and tobacco, as described in said Herbicide Handbook.
Each of the thiocarbamate herbicides described, which are representative of the S-alkyl, dialkylthiocarbamates wherein alkyl contains 2 to 6 carbon atoms and is straight chained, branched or cyclic, have an upper dosage limit when applied to valuable crops. In the case of butylate, a commercially sold composition of the herbicide contains the antidotal compound N,N-diallyl-2,2-dichloroacetamide, also commonly known as R-25788, which safens the action of the butylate toward corn, e.g., substantially without affecting its herbicidal properties against weed species, permitting the use of a somewhat higher, more effective, dosage rate. This antidotal compound also safens the other thiocarbamates towards valuable crops which show at least some tolerance to these herbicides.
2-(2,2,2-Trichloroethyl)-2-(3,5-dichlorophenyl)oxirane is a herbicide active against annual grassy weeds. Such compound is described in Canadian Patent 1,040,642 and British Patent 1,469,741. This oxirane compound is prepared by epoxidation of 2-(3,5-dichlorophenyl)-(4,4,4-trichloro)-butene-1 with a percarboxylic acid, e.g., peracetic acid, preferably in the presence of a buffer solution of the acid reactant, e.g., sodium acetate with peracetic acid. In carrying out the reaction the chlorophenyl substituted butene is usually blended with a solvent medium such as methylene chloride or 1,2-dichlorobenzene and mixed slowly with the percarboxylic acid-buffer solution. A suitable ratio of reactants is in the range of one mole of the butene compound to one to six moles of percarboxylic acid. Reaction proceeds rather slowly at a modest temperature of about 20.degree. to 40.degree. C. and ambient atmospheric pressure over a period of about 24 to 100 hours or more. The oxirane is recovered upon, e.g., washing the reaction mixture with water and neutralizing it with a base such as sodium carbonate, drying the oil over anhydrous sodium sulfate, and concentrating the residue under reduced pressure.
The use of nitrapyrin, i.e., 6-chloro-2-trichloromethylpyridine and related chloropyridines having a trichloromethyl substituent on the ring for the suppression of nitrification of ammonium nitrogen is described and claimed in U.S. Pat. No. 3,135,594. The preparation of such compounds or close analogs or isomers is described in U.S. Pat. Nos. 3,224,950; 3,296,272; 3,418,323; 3,420,833 and 3,424,754, the teachings of which are incorporated herein by reference. In general, preparation of these compounds involves high temperature chlorination of alpha-picoline, gamma-picoline, 2,6-dimethylpyridine, 2-chloromethylpyridine or aminochloropyridine in which the pyridine compound is contacted by gaseous chlorine at a temperature of about 100.degree. to 165.degree. C. until the requisite degree of chlorination is achieved in the ring or the side chain, and the resulting isomers, homologs or analogs separated.
A chloropyridine with an active chlorine in one of the 2 or the 4 position and a chloromethyl group in the other of the 2 or 4 positions is reacted with a nitrogen base such as ammonia or an aliphatic acyclic or heterocyclic amine, usually with an amount of the base in excess of the stoichiometric amount, and at a temperature of about 80.degree. to 110.degree. C. for about 30 to 120 minutes, after which the reaction mixture is allowed to cool and the desired product is recovered by extracting or washing out the unreacted base with water.
Alkylthiochloropyridines or alkylthiochloro-chloromethylpyridines are prepared by reacting an alkali metal mercaptan with a 4-chloropyridine or 4-chloro-chloromethylpyridine at a temperature of about 60.degree. to 100.degree. C. The alkylthiochloropyridine or alkylthiochloro-chloromethylpyridine compounds are converted to the corresponding sulfonyl compounds by oxidation with fuming nitric acid, nitric acid, hydrogen peroxide, potassium permanganate or a mixture of alkali metal chromate and sulfuric acid. Generally a temperature of about 15.degree. to 120.degree. C. suffices though the use of either hydrogen peroxide or nitric acid as oxidizing agent requires a higher minimum reaction temperature of the order of 75.degree. or 80.degree. C.